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Water Pump / Pressure Tank Help


Overland
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I just got finished installing a Flotec 2 gallon pressure tank/accumulator and am having an issue with the pump short cycling. The Shurflo water pump in my trailer is the 4008-101-A65 (which should be the same as any one else's) and the documentation shows a cutoff pressure of 55 psi and restart of 40 psi. So with that info in hand, I set the precharge pressure of the tank to 38 psi. Hooked it all up and turned the pump on and it cycled on and off fairly quickly, like normal. Obviously it wasn't filling the tank, so I ran some water and sure enough the pump started right up. So I started lowering the pressure of the tank until the pump kicked on, which was about 28 psi and the pump ran until the tank got to 39 psi and the pump shut off. I repeated this several times and the pressures were the same.

 

So, is the pressure switch on my pump set to 28/39? That can't be right. I'm measuring from the tank rather than directly, so maybe I need to go get an inline pressure gauge to verify the numbers. Regardless, as it is I'm only getting 5 cups of water from the tap before the pump kicks in and I'm pretty sure I should be getting close to the 2 gallon capacity of the tank.

 

Any ideas?

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Yes, Flotec recommends the same 2 psi below the cut in pressure.

 

So I discovered on the Shurflo pump that there's a little 2mm hex screw on the pressure switch that you can adjust. I was able to adjust it so that the gauge read 55 psi, but the pump seemed to have a bit of trouble getting that last 5 psi. Cut-in at that setting was a little below 40 psi, so at least according to my gauge, it was close to spec. The problem is that even at that pressure I'm still only getting 5 cups of water before the pump kicks in.

 

I'll have to search again, but I thought someone here said that with the Flotec tank they were able to get an entire shower out of it without the pump starting. Good for them if they can take a 5 cup shower, but if not, then perhaps there's something wrong with my tank? I can't think what it would be though. Perhaps the bladder isn't expanding enough?

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Will do, thanks. I'm letting it sit for a while at the higher pressure to see if maybe the bladder is stiff and not expanding enough. I tried lowering the pre-charge down to 10 psi to see if perhaps it needed a bit of a push to get it working. That may have helped some as I seem to be getting closer to 6 cups out of it now before the pump cycles on.

 

If I cut the pump and just let the water run, I get about 1.5 gallons out of the tank before it peters out. That's a half gallon less than the tank capacity but I imagine some water will always remain behind and the pre-charge and bladder will take up some of that room.

 

Even if I can't fix it, 6 cups is 6 cups, which is better than nothing. It keeps the pump from going tump tump tump when the water is turned on just a bit, which is all I really wanted.

 

I'll give Flotec a call in the AM.

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Overland -

Since I didn't get a chance to test mine sine the install I sure do hope you get this figured out within the next week or so. Sorry I'm of no help but I think that Mark (and you) are on the right track for getting to the bottom of the issue.

Bill

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2017 Ford F150 Lariat 3.5EB FX4 Max Towing 2016 Oliver Elite II - Hull #117 "Twist"

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I just got finished installing a Flotec 2 gallon pressure tank/accumulator and am having an issue with the pump short cycling. The Shurflo water pump in my trailer is the 4008-101-A65 (which should be the same as any one else’s) and the documentation shows a cutoff pressure of 55 psi and restart of 40 psi. So with that info in hand, I set the precharge pressure of the tank to 38 psi. Hooked it all up and turned the pump on and it cycled on and off fairly quickly, like normal. Obviously it wasn’t filling the tank, so I ran some water and sure enough the pump started right up. So I started lowering the pressure of the tank until the pump kicked on, which was about 28 psi and the pump ran until the tank got to 39 psi and the pump shut off. I repeated this several times and the pressures were the same.

So, is the pressure switch on my pump set to 28/39? That can’t be right. I’m measuring from the tank rather than directly, so maybe I need to go get an inline pressure gauge to verify the numbers. Regardless, as it is I’m only getting 5 cups of water from the tap before the pump kicks in and I’m pretty sure I should be getting close to the 2 gallon capacity of the tank.

Any ideas?

 

My pump actually runs at a lower pressure than it's specs say too. No big deal assuming you don't want to firehose something and you don't have the tankless WH. It doesn't matter where you measure the static pressure in the system as long as it's downstream of the pump, but a long restrictive pigtail connector before the accumulator will make the pump stutter as it tries to shut off.

 

You are adjusting the tank pressure in the right way. Matching the pump's actual pressure settings and allowing the accumulator to partially fill before the pump shuts off. There is no problem with the bladder and you are doing it correctly, but you will never get anywhere near two gallons out before the pump cycles. A 2 gallon tank will only yield a few cups before the switch differential is reached. It's not there to hold a lot of water, but to stabilize the pressure and reduce the number of cycles. If the bladder presssure was at zero, the tank would not work at all and if the pressure was above pump shutoff it, again, would not work at all. It should be set just below the cut-in pressure. This gives you a fairly large amount of water in the tank, for fewer cycles, and it allows for the expansion of the water caused by warming of the water heater. A good test is 1. install a 100 PSI pressure guage on the pressure side of the pump (a good plce for this is a T on the pump outlet or a T on the accumulator inlet). 2. get all air out of the water system by running the water until no air is present. 3. run the faucet to turn on the pump, shut off the faucet and allow the pump to reach full cut-off pressure with no water running. Don't run any more water. 3. then turn on the water heater and monitor the pressure on a guage.

 

This will cause the pressure to rise. The more air volume in the tank, the less the rise. If you start a test about 40 PSI (the cut-out pressure), you should reach about 60 PSI or less as the water heater comes up to full temp. With no accumulator, the pressre will go up over 100 PSI and pop the relief valve.

 

Overall, just find a happy medium tank pressure that allows minimal pump cycles and keeps the pressure as steady as possible while the water heater goes from cold to hot. This will be somewhere just below the cut-in pressure.

 

All piping between the pump outlet and the accumulator should be short and relatively large in diameter. If not, the pump will stutter as it approaches the cut-off point.

 

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John


"I only exaggerate enough to compensate for being taken with a grain of salt."


LE2 #92 (sold),   Black Series HQ19   

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Thanks John. Reading through the manual, I realized that the draw down, or amount you'll actually get from the tank is supposed to be from 0.5 to 0.7 gallons, depending on the pressure, and I'm only getting about half that. I'm thinking now that the difference is that on their chart, they say 0.5 gallons for 40-60 psi, which I assume is cut-in/cut-out pressures. That's a 20 psi difference and what I'm measuring, regardless of the pressure I set, is closer to 10 psi. I think if I were getting the 15 psi differential per spec on the Shurflo, I'd get closer to what I should be getting.

 

Like I said, I'm happy with it as it is, though I'd like to get the most out of it. Installing it was a true pain in the rear. You look at it and think yeah, that would go in a half dozen places, but it does not.

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Overland,

 

You're right. The lower the differential pressure in the pump switch, the less water will be available from the accumulator before the next pump cycle occurs. However, the larger the differential, the more pressure variation you'll experience at the faucet or shower head. Once you have the tank pressure set at just below the cut in pressure you are doing the best with the tank you have and the volume is just related to the tank size. Once you get a tank large enough to stabilize the system, a larger one just makes longer pump cycles. Remember, the pump will run just as much overall, but it will do it in longer cycles, when more water is stored in the accumulator. Shorter cycles mean less noticeable pressure differences, longer cycles mean larger apparant pressure changes at the faucet. The function is to stabilize the pressure through temp changes and to keep the pump from short cycling. Beyond that is just a trade of one aspect for another.

 

I was considering a larger tank, but went with the little RV size. It's just barely big enough to keep the pressure rise from the water heater under control if set at just the right pressure. A bit too small for my liking, so I'll probably go to a #5 size domestic expansion tank. The #8 is a common size used in houses. Bigger is harder to locate and mount, as you seem to have noticed.

 

If you need to mount the tank farther from the pump, which is normally a problem, there is a trick that will probably allow it using a waterhammer arrester teed in at the pump outlet, and then mounting the accumulator somewhere else farther away than normal.

 

Another small benefit of the accumulator I notice is after I shut off the pump switch, as I lke to do normally, I can still get some water without switching it back on. This might get a glass of water or flush the toilet without running the pump. Quieter in the middle of the night.

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John


"I only exaggerate enough to compensate for being taken with a grain of salt."


LE2 #92 (sold),   Black Series HQ19   

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That was the tank I installed a couple years ago, when I had my water pressure woes. My thinking was that I was looking for less cycling, so I went with more split. If I was in a house and running a continuous shower, then the pressure difference would be annoying, but with taking navy showers, it isn't as noticable with all the off and on. Back then I checked to see how long (time wise) I could get before cycling and learned to "feel" when it would start so that it would be during an off part of the shower when it would refill the tank. I never actually checked the drawdown spec.

 

At the kitchen sink, the pressure difference doesn't matter at all to me and I've never really noticed. Each of us being able to use the head in the middle of the night with having to run the pump was also part of the consideration, so just make sure the pump has run before shutting it off.

 

Where did you put it that it was so much trouble?

 

Edit- I see your maintaining this in two different threads. I didn't think Flotec made a 6 gallon horizontal tank, and they do make horizontal specific tanks, so mounting it in a horizontal configuration may adversely affect it's operation.

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Randy


One Life Live It Enjoyably


2017 F350 6.7L SRW CC LB


2015 Oliver Elite II Hull #69

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It’s just a 2 gallon tank. They label it at it’s non-pressurized “equivalent” capacity. We do navy showers also - hadn’t thought of being able to time rinsing with the pump. This may then be ideal for that. And since we now know the draw down we’ll have a better idea of how much water we’re using.

 

The problem we were having at the kitchen faucet is that we rinse dishes under a slow stream to try to conserve water. The pump would cycle every second and the water would spurt. This allows a nice even stream of water and probably for long enough to rinse several dishes. I suspect we’ll develop a technique for both dishes and showers to work with the pump cycles.

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John, I have had pulsing drips from the water heater pressure valve before, so perhaps this will fix that.

 

I won’t have to move the tank. It’s right at the pump and access is good. It was just difficult to get it in that spot as I had to move some water lines to get it in place. Once in that spot it actually has a good amount of wiggle room, though fastening it in place was tricky. Anyway, the pump doesn’t sputter at all.

 

Good thought on using water with the pump off. I can get 1.5 gallons that way so plenty for nighttime or occasional use.

 

Thanks for all the replies. I think if there’s an improvement to be made it will be with the pump, but all of this advice on how to get the most out of the tank has been great and I think we’ll really enjoy having it.

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I talked to Shurflo and unfortunately, they consider anywhere from a 7 to 25 psi differential between cut-in and cut-out to be within spec. That's the spec on the pressure switch that they buy and isn't anything that can be adjusted. Luck of the draw, I got 10. They agreed that it was the lower differential that was limiting what I'm getting from the pressure tank. I guess I could go buy 100 pumps, pick the best, and send 99 back, but otherwise, I'm stuck.

 

That's a tremendous variation, meaning that each of us could have vastly different experiences with the pump. It's probably the reason why the cycling on ours bothered us while other people don't mind. But I guess a smaller differential would be preferable to some, since the pump would kick on with very little pressure change in the system. So perhaps what I've got, an overly sensitive pump but a pressure tank that cuts down on the cycling, is better than a less sensitive pump that allows more draw down between cycles.

 

They did help me diagnose that the bypass on the pump was also set unusually low, which was why it struggled when I set it to 55 psi. Makes me wonder if Oliver doesn't fiddle with these to keep the pressures down. That, or quality control at Shurflo is pretty lousy. Anyway, adjusting that should help the pump and they said I could actually close off the bypass entirely since I've added a pressure tank.

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  • 2 years later...

"Anyway, adjusting that should help the pump and they said I could actually close off the bypass entirely since I've added a pressure tank."

Overland, I'm intrigued by this statement. What does it mean to close off the bypass of a Shurflo 4008? Does one simply tighten the bypass pressure screw until it's fully seated? I have a 2 gallon pressure tank installed but looking to improve its functionality. (IE: one toilet flush at night still activates the pump...)

Regards, GK

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How much pressure is in the bladder on the tank?  I would imagine there is a cover for a Schrader valve where you can add or release air from the bladder.  Maybe there is insufficient pressure in the bladder that accounts for more cycling.

David Caswell and Paula Saltmarsh


Hull 509 "The Swallow"

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